The present invention relates to a device and method for triggering a random event. In particular, but not exclusively, the present invention is concerned with a device and method for triggering a random win event suitable for use in a Pachinko gaming machine employing a radioactive random pulse generator.
The use of a Radioactive Random Pulse Generator (RPG) in a Pachinko Gaming Machine has been previously described in Japanese Patent Application JP 6-154411. The purpose of the RPG is to randomly trigger a win event when a ball bearing enters a metal xe2x80x9ctulipxe2x80x9d in the Pachinko machine. According to JP 6-154411 the Pachinko machine measures the output of the RPG for 1 second when a ball enters a metal tulip in the machine. The player wins if the output of the RPG equals a xe2x80x9cnumberxe2x80x9d which has been pre-programmed into the machine at the factory.
The probability of a win is fixed at the factory by the Pachinko machine manufacturer to comply with guidelines agreed with the parlours and the police authorities. The odds of a xe2x80x9cbig winxe2x80x9d is typically set to be about 1/220. The output of the RPG is completely random and unpredictable but on average there will be two possible outputs which will occur once every 220 measurements. The Mean RPG output is measured by counting the output of the RPG at the factory for a long time. Poisson or Gaussian probability theory is then used to calculate which of the many possible outputs will have a 1/220 probability of occurring. This output is the xe2x80x9cnumberxe2x80x9d which is programmed into the Pachinko machine for triggering the win events.
Although this is an elegant method of triggering random win events with a predetermined probability, there are some practical difficulties with the method. In order to set the win probability to 1/220 within a tolerance of +/xe2x88x925% it is necessary to carry out particularly accurate measurements of the Mean RPG outputs. The accuracy required for this is about 0. 1%-0.3% of the Mean. This requires long measurement times of up to several hours for each RPG. This is a major practical drawback. The present invention provides an improvement to JP 6-154411 in so far as the measurement time and measurement accuracy of the Mean are concerned.
The radioactive content of the RPG described in JP 6-154411 is xcx9c1 xcexcCi. This gives rise to regulatory and safety concerns about the use of this amount of radioactivity in RPG devices. The present invention provides a significant improvement in that the radioactive content can be reduced by at least 100 times and up to 100,000 times. The lower activity content reduces radiation damage and degradation of the sensitive detector and this contributes to superior performance and stability over long periods of operation. For various regulatory, safety and operational reasons it is also highly desirable to minimise the amount of radioactivity required to operate the RPG. Preferably the activity should be  less than  less than 0.1 xcexcCi. This is not possible using the device described in JP 6-154411.
Furthermore, it is an easy matter to select and set any desired win probability at the factory using the present invention. This may be in the range of about 1/5 to 1/1000 which is ideal for gaming applications. Variable win probability over this wide range is not possible using the method described in JP 6-154411.
The present invention provides a method of triggering random events comprising on a plurality of occasions detecting individual radiation decay events, counting the number of detected events within a predetermined period of time and storing the numbers of events counted; comparing the stored numbers of events; and triggering a random event in dependence on whether at least two of said stored numbers of events are equal.
In one embodiment the counter only determines whether said number of decay events is non-zero whereby said random event is triggered in dependence on both the stored number of events and the one or more new numbers of events being non-zero.
In a further aspect the present invention provides a device for triggering a random event comprising at least one radiation detector, a counter for counting the number of radiation decays detected within a predetermined time interval, comparator means for comparing at least two numbers of decay events detected and an event trigger for triggering a random event in dependence on the at least two numbers of decay events being equal (see FIG. 1).
In a preferred embodiment the device further including at least one source of radiation.
In a third aspect the present invention provides a random win event generator adapted for use with a Pachinko gaming machine comprising a device as described above.
With the present invention the activity content of the device may be  less than xcx9c5 nCi which is below the internationally accepted contamination and leak test limits which apply to the sale and use of sealed radiation sources. Moreover, in comparison to the RPG described in JP 6-154411, the activity content of the device in accordance with the present invention may be reduced by a factor of between about 100 and 100,000 depending on how the Pachinko machine is programmed. The very low activity possible with the present invention reduces the rate of radiation degradation and drift in the long term performance of the PIN diode detector which is contained within the RPG. The very low activity also gives rise to alternative manufacturing and design possibilities for the device as an RPG. In particular, electrical deposition and direct dispensing from standardised 241Am solutions are possible. These methods provide potential manufacturing advantages.
In addition, when the device and method of the present invention are used in a Pachinko gaming machine in the form of an RPG the degree of accuracy needed in measuring the output of individual RPGs for the purpose of calculating and programming a xe2x80x9cfixed numberxe2x80x9d is reduced. A large tolerance on the RPG output is permissible with the present invention. For example xcx9c9% uncertainty in the Mean RPG output can give as little as xcx9c5% uncertainty in the win probability depending upon the particular type of measurements taken. Even in the worst cases with the present invention the tolerances are no worse than about a quarter of this.
A major advantage of the present invention is that the large tolerance which is permitted on the device output enables all devices to be manufactured so that the same fixed numbers can be programmed whereas the RPG described in JP 6-154411 requires a unique xe2x80x98fixed numberxe2x80x99 to be calculated for each RPG by measuring the Mean output of each RPG accurately. With the present invention on the other hand it is only necessary to ensure that the manufacturing process is capable of achieving an overall batch tolerance of +/xe2x88x929% in the case of the preferred embodiment. This avoids the need to measure the outputs of individual devices or to calculate any specific xe2x80x98fixed numbersxe2x80x99.
Although a probability 1/220 is given as the desired probability in the forthcoming examples, it will be understood that by appropriate selection of the measurement time interval and the number of repeated measurements taken, any desired probability can be achieved. Moreover, in accordance with the present invention the device for triggering a random event may be programmed so that when input with the desired probability the device automatically determines the appropriate measurement parameters.